1. Field of the Invention
The present invention relates to a system of soldering and particularly to an improved nozzle assembly used to deposit solder in a precise manner, as where solder is deposited onto solder wettable contact pads utilized in the semiconductor industry.
2. Description of the Prior Art
Solder distribution onto mounting pads for surface mount boards of the type used in the semiconductor industry has generally been accomplished in the prior art through the use of screening processes. In these techniques, art work and screens are fabricated having the solder deposition pattern. Then, a precision alignment process is carried out wherein the solder is screened onto the surface mount pads. The solder paste used for this process requires a substantial cure time and a substantial bake time. Various problems result due to the complexity of the alignment process making the prior art technique relatively time consuming.
The prior art technique utilizing screening is further complicated by a requirement that the pattern mixes very fine lead pitch and width surface mount pads along with standard surface mount parts. For example, in the case of tape automated bonding, the pitches vary from about 4 to 20 mils while, the standard surface mount parts have pitches in the range from about 20 to 50 mils. Due to the precision nature of the operation, it is common to utilize separate screening steps, one for the very fine lead pitch and width surface mount parts and second for the standard surface mount parts. There is the possibility of damaging the solder deposited in a previous step when multiple screening operations are carried out. Additionally, screening fine line solder represents a problem because the solder paste tends to stick in the openings of the screen as the openings get progressively narrower.
The prior art screening systems also present problems due to the difficulty of performing rework operations. Once a defective part has been removed, there is no commonly available technique for replacing the solder on the board site. While techniques exist to remove the solder after the part has been removed, replenishing the isolated site by screening is not generally feasible.
The present invention has as its object to provide a device which is usable either manually or under robotic control to deposit solder onto fine line pitch and width surfaces in precise fashion.
Another object of the invention is to deposit solder onto solder wettable contact pads with substantially uniform amounts on each pad.
Another object of the invention is to provide a device for depositing solder on pads of surface mount board without the requirement for artwork or solder screens.
Another object of the invention is to define a system employing a device which will apply solder in a fine line pattern to a circuit card.
Another object of the invention is to provide a two-piece nozzle with a lower section which is easily removeable for cleaning and maintenance.
Another object of the invention is to provide a solder placement nozzle in which the soldering iron operating temperature is lowered by properly insulating the soldering iron within the surrounding nozzle housing.
Another object of the invention is to provide a solder placement nozzle having a removeable wettable ring portion to facilitate periodic cleaning and maintenance.
Another object of the invention is to provide a solder placement nozzle which merges the application of flux and an inert cover gas at the solder application site through the use of extension tubes which merge and incorporate these functions.